During development and differentiation, keratinocytes traffic a variety of receptors and junctional components to their plasma membrane. Much of the work has focused on the temporal and spatial delivery of these components while little study has focused on the mechanism of intracellular trafficking. I am proposing to study the dynamics of Rab25 during keratinocytes differentiation using in vitro cell culture models. The initial work will characterize the dynamics of Rab25 induction in response to calcium and identify any known components of the apical recycling system that also exhibit altered expression in response to calcium concentration. Once we have established a method of differentiation of the Balb/MK cells potential cargoes can be co-stained for with Rab25, these would include transglutaminase and growth factor receptors, such as keratinocyte growth factor receptor. These results will form a guide that will allow us to evaluate the Rab25 KO mice. We know of no other studies that are investigating in general the role of the apical recycling system and specifically the role of the Rab11 family of GTPases in skin differentiation. While our laboratory has great experience in the investigation of apical recycling in polarized epithelial cells this is a new model system for us. This work should provide insight into the impact of trafficking pathways on skin differentiation and potentially on apical recycling in general.